First-principles Study On Magnetic And Electronic Structures Of Lanthanum-based Perovskite-type Heterointerfaces

In recent years,perovskite oxide heterointerfaces can combine ferroelectricity and ferromagnetism to produce various forms of multiferrosity.Due to the breaking of the symmetry of the oxide interface,the coupling of degrees of freedom such as spin,orbit,charge,and lattice at the oxide interface can generate various novel physical properties such as superconductivity,magneto-electric coupling（MEC）,and two-dimensional electron gas（2DEG）.These properties can be applied to fields such as low-power devices,advanced data storage,and fast read and write devices.It has been developed in various nanoscale devices,receiving extensive attention from researchers.In this thesis,the first-principles method based on density functional theory（DFT）was used to study the interfacial magnetism and electronic structure of（La Fe O₃）_m/（Sr Fe O₃）_n and（La VO₃）_m/（Sr VO₃）_n perovskite oxide heterointerfaces in detail.Firstly,This article establishes（LaFeO₃）_m/（SrFeO₃）_n and（LaVO₃）_m/（Sr VO₃）_nheterointerfaces to study the effects of different oxide layers on the magnetic and electronic structures（Spin,Orbit,Charge）of interfaces.This research found that changes in the number of layers of the two substrates at the heterogeneous interface can lead to the transition of the magnetic ground state,and may exhibit magnetic structures that do not exist in their bulk oxides.The（La Fe O₃）_m/（Sr Fe O₃）_n heterogeneous interface exhibits A-type and C-type antiferromagnetic structures other than the G-type antiferromagnetic state of the bulk crystal structure La Fe O₃ and the ferromagnetic state of Sr Fe O₃.（La VO₃）_m/（Sr VO₃）_n exhibits A-type and G-type antiferromagnetic states in addition to the C-type antiferromagnetic states of the bulk crystal structure La VO₃ and the ferromagnetic states of Sr VO₃.At the same time,in the two heterogeneous interface systems of（La Fe O₃）_m/（Sr Fe O₃）_n and（La VO₃）_m/（Sr VO₃）_n,the microstructure of the heterogeneous interface exhibits a transition from metal to half-metal with the change of the number of substrate layers,indicating that the interface effect has a significant impact on the magnetic and electronic structure（Spin,Orbit,Charge）of the perovskite heterogeneous interface.In addition,oxygen vacancy defects can effectively modulate the electronic structure of heterogeneous interfaces,enhance electron enrichment,and change the charge transfer ability of materials.In order to clarify the role of oxygen vacancies in（La Fe O₃）_m/（Sr Fe O₃）_n and（La VO₃）_m/（Sr VO₃）_n heterointerfaces in experimental studies,This article introduced an oxygen vacancy in the Fe O₂ and VO₂ layers at the interface respectively,and studied the magnetic ground states and electronic structures of the heterointerfaces containing oxygen vacancies.This research found that the introduction of oxygen vacancies at the interface changed the magnetic ground state and electronic structure（Spin,Orbit,Charge）of most heterogeneous interfaces.This demonstrates that oxygen vacancies have a significant impact on the magnetic ground state and electronic structure（Spin,Orbit,Charge）of the heterogeneous interface.Therefore,this research find that changing the thickness of the oxide layers in the heterogeneous interface and introducing oxygen vacancy defects in the interface layer can effectively modulate the magnetic and electronic structure of the heterogeneous interface,and even lead to the generation of two-dimensional electron gases at the interface,which may be accompanied by a transition from metal to half-metal.This work will provide new research ideas for the design and related experimental research of oxide heterogeneous interfaces with unique properties.